High Energy DIS after HERA?… The LHeC Project (Ee=140GeV and Ep=7TeV) Paul Newman (Birmingham University) Southampton Seminar 18 June 2010 … work in progress from ECFA/CERN/NuPECC workshop on ep/eA physics possibilities.
Download ReportTranscript High Energy DIS after HERA?… The LHeC Project (Ee=140GeV and Ep=7TeV) Paul Newman (Birmingham University) Southampton Seminar 18 June 2010 … work in progress from ECFA/CERN/NuPECC workshop on ep/eA physics possibilities.
High Energy DIS after HERA?… The LHeC Project (Ee=140GeV and Ep=7TeV) Paul Newman (Birmingham University) Southampton Seminar 18 June 2010 … work in progress from ECFA/CERN/NuPECC workshop on ep/eA physics possibilities at the LHC http://cern.ch/lhec Overview LHeC is the latest and most promising attempt to take ep Physics into the TeV centre-of-mass scale … - Status of ep Physics after HERA - How to build an ep Collider using the LHC - Physics motivation - BSM physics - Precision QCD / EW - Low x / high parton densities - Detector considerations - Timeline and outlook Basic Deep Inelastic Scattering Processes Neutral Current Q2 = -q2 (q) Charged Current (q) :resolving power of interaction x = Q2 / 2q.p : fraction of struck quark / proton momentum Collage of “Text-Book” HERA Plots HERA’s most famous legacy Parton densities of proton in an x range well matched to the LHC rapidity plateau Some limitations: - Insufficient lumi for high x precision - No deuterons … u and d not separated - No heavy ions - No time to fully explore new concepts like GPDs, DPDFs, unintegrafed PDFs • H1/ZEUS/joint publications still coming for 1-2 years • Further progress requires higher energy and luminosity … HERA-LHC Workshop … (see also PDF4LHC) (270 participants) (150 participants) Workshop on the implications of HERA for the LHC (partons, jets, heavy flavours, diffraction, MC tools …) 807 pages! (March 2009) (160 participants) (190 participants) Currently Approved Future of High Energy DIS Some LHeC Context The LHeC is not the first proposal for TeV scale DIS, but it is the first with the potential for significantly higher luminosity than HERA … … achievable with a new electron accelerator at the LHC … [JINST 1 (2006) P10001] The Electron-Ion Collider (BNL / Jlab) e.g. 10 GeV e+/- and 250 GeV polarised p/A - Limited in energy but 100 times HERA luminosity - Polarised hadrons spin long-term successor to HERMES, COMPASS?… - Heavy ions huge step forward for eA kinematic range [More info at http://web.mit.edu/eicc] LHC is the future of the high energy frontier! “… the LHeC is already half built” [J Engelen] Can its unprecedented energy and intensity be exploited for DIS? “… it would be a waste not to exploit the 7TeV beams for ep and eA physics at some stage during the LHC time” [G. Altarelli] How Could ep be Done using LHC? … whilst allowing simultaneous ep and pp running … RING-RING LINAC-RING • First considered (as LEPxLHC) in 1984 ECFA workshop • Previously considered as `QCD explorer’ (also THERA) • Main advantage: high peak lumi obtainable (~3.1033 cm-2 s-1) • Main advantages: low interference with LHC, high Ee ( 150 GeV?) and lepton polarisation, LC relation • Main difficulties: building round existing LHC, e beam energy (60GeV?) and lifetime limited by synchrotron radiation • Main difficulties: lower luminosity ~3.1032 cm-2 s-1 (?) at reasonable power, no previous experience exists Accelerator Design Multi-Institute / Lab Involvement Novosibirsk, BNL, CERN Cockcroft, Cornell, DESY, EPFL Lausanne, KEK, Liverpool, SLAC, TAC Turkey • Design constraints of simultaneous ep and pp running, power consumption < 100 MW • 100 fb-1 at Ee = 60 GeV looks to be possible with a few years running The Luminosity v Acceptance Question • As for HERA-I v HERA-II, low b focusing beam elements around interaction region can improve lumi by a factor ~10 • However, acceptance near beam-pipe is compromised loss of low x / Q2 acceptance loss of high Meq acceptance poorer HFS measurements Beam Scenarios for First Physics Studies Several scenarios under study … see later for justification ep Studies based on a 20-150 GeV electron beam and lumi of 1-10 fb-1 / year Scenario for Experimental Precision Requirements to reach a per-mille as (c.f. 1-2% now) … [Klein, Kluge …] The new collider … - should be ~100 times more luminous than HERA The new detector - should be at least 2 times better than H1 / ZEUS Lumi = 1033 cm-2 s-1 Acceptance 10-170o (179o?) Tracking to 0.1 mrad EM Calorimetry to 0.l% Had calorimtry to 0.5% Luminosity to 0.5% (HERA 1-5 x 1031 cm-2 s-1) (HERA 7-177o) (HERA 0.2 – 1 mrad) (HERA 0.2-0.5%) (HERA 1%) (HERA 1%) First `pseudo-data’ for F2, FL, F2D …produced on this basis … Kinematics & Motivation (140 GeV x 7 TeV) New physics on scales ~10-19 m Large x partons High precision partons in LHC plateau High Density Matter Nuclear Structure & Low x Parton Dynamics s 2 TeV • High mass (Meq, Q2) frontier • EW & Higgs • Q2 lever-arm at moderate & high x PDFs • Low x frontier novel QCD … x 107 at 2 2 Q 1 GeV Searches For New Physics • The (pp) LHC has better discovery potential than the LHeC in the majority of scenarios (and is already running!) • However, LHeC is competitive with (or better than) LHC in cases where initial state lepton is an advantage … and who knows what will happen – nature may hold surprises! Searches For New Physics • The (pp) LHC has better discovery potential than the LHeC in the majority of scenarios (and is already running!) • However, LHeC is competitive with (or better than) LHC in cases where initial state lepton is an advantage … and who knows what will happen – nature may hold surprises! Lepton-quark Bound States • Leptoquarks appear in many extensions to SM… explain apparent symmetry between lepton and quark sectors. • Scalar or Vector color triplet bosons carrying L, B and fractional Q, complex spectroscopy? • (Mostly) pair produced in pp, single production in ep. • LHeC sensitivity (to ~1.5 TeV) similar to LHC, but can determine quantum numbers / spectroscopy (fermion #, spin, chiral couplings …) Yukawa coupling, l (Zarnecki) (10 fb-1) LHeC LHC pair prod Rp Conserving Supersymmetry in pb, e- p in pb, e+ p (Perez) e q ~ e 0 ~ q Pair production via t-channel exchange of a neutralino. Cross-section sizeable for SM < 1 TeV i.e. if squarks are “light”, could observe selectrons up to ~ 500 GeV, a little beyond LHC? Excited Leptons [Sauvan, Trinh] LHeC gives best sensitivity in this scenario … Complementarity between LHC and LHeC Contact interaction term introduced in LHC pseudo-data for high mass Drell-Yan [Perez] • Even if new physics looks rather different from SM, wide range of high x BSM effects can be accomodated in DGLAP fits due to poor current high x PDF constraints • Better high x precision at high lumi LHeC could disentangle … Higgs Production [U Klein, Kniehl, Perez, Khuze] Sizeable CC (WW) x-section ~ few thousand events Strongly dependent on mH Novel production mechanism Clean(ish) … H + j + ptmiss bbbar coupling to light H? Forward acceptance is an issue First background studies (jets in CC) underway … LHeC Impact on High x Partons [Kluge, Perez, Klein] Full NC/CC sim (with systs giving per mille as ) & NLO DGLAP fit using HERA technology… … full flavour decomposition possible … high x pdfs may help clarify LHC discoveries through interpretation of new states? [Some of highest x improvement from paramn extrapolation] PDFs & EW Couplings [Gwenlan] Using ZEUS fitting code, HERA + LHeC data … EW couplings free Ee = 100 GeV, L = 10+5 fb-1, P = +/- 0.9 ZEUS Cross Sections and Rates for Heavy Flavours HERA Charm [Behnke] 27.5 x 920 Beauty cc sW-> c bW->top ttbar c.f. luminosity of ~10 fb-1 per year … Flavour Decomposition High precision c, b measurements (modern Si trackers, beam spot 15 * 35 m2 , increased HF rates at higher scales). Systematics at 10% level beauty is a low x observable! s (& sbar) from charged current Similarly Wb t? b LHeC 10o acceptance s LHEC 1o acceptance [Mehta, Klein] (Assumes 1 fb-1 and - 50% beauty, 10% charm efficiency - 1% uds c mistag probability. - 10% c b mistag) Low-x Physics and Non-linear Evolution • Somewhere & somehow, the low x growth of cross sections must be tamed to satisfy unitarity … non-linear effects • Dipole model language projectile qq multiply interacting • Parton level language recombination gg g? • Usually characterised in terms of an x dependent “saturation scale”, Q2s(x), to be determined experimentally Non-linear effects in HERA and eA Data? Something appears to happen around t = Q2/Q2s = 1 GeV2 (confirmed in many analyses) BUT … Q2 small for t <~ 1 GeV2 … not easily interpreted in QCD Lines of constant ‘blackness’ diagonal … scattering cross section appears constant along them … “Geometric Scaling” Strategy for making the target blacker LHeC delivers a 2-pronged approach: Enhance target `blackness’ by: 1) Probing lower x at fixed Q2 in ep [evolution of a single source] 2) Increasing target matter in eA [overlapping many sources at fixed kinematics … density ~ A1/3 ~ 6 for Pb … worth 2 orders of magnitude in x] 30 Basic Inclusive Kinematics / Acceptance Access to Q2=1 GeV2 in ep mode for all x > 5 x 10-7 IF we have acceptance to 179o (and @ low Ee’) Nothing fundamentally new in LHeC low x physics with q<170o … low x cross sections are large! … luminosity in all realistic scenarios ample for most low x measurements Some models of low x F2 with LHeC Data With 1 fb-1 (1 year at 1033 cm-2 s-1), 1o detector: stat. precision < 0.1%, syst, 1-3% [Forshaw, Klein, PN, Soyez] Precise data in LHeC region, x > ~10-6 - Extrapolated HERA dipole models … - FS04, CGC models including saturation suppressed at low x & Q2 relative to non-sat FS04-Regge … new effects may not be easy to see and will certainly need low Q2 (q 179o) region … FL Simulation Vary proton beam energy as recently done at HERA ?… ‘direct’ gluon measurement … Ep (TeV) ---------7 4 2 1 [0.45 Lumi (fb-1) ----------1 0.8 0.2 0.05 0.01] … precision typically 5% … stats limited for Q2 > 1000 GeV2 … could also vary Ee … … selected lowest x data compared with 3 dipole models including saturation … [Forshaw, Klein, PN, Soyez] Extrapolating HERA models of F2 (Albacete) NNPDF NLO DGLAP uncertainties explode @ low x and Q2 Formally, wide range of possibilities allowed, still fitting HERA • ‘Modern’ dipole models, containing saturation effects & low x behaviour derived from QCD give a much narrower range • c.f. 2% errors on LHeC F2 pseudo-data, 8% on FL pseudo-data … we should be able to distinguish … Fitting for the Gluon with LHeC F2 and FL (Gufanti, Rojo …) HERA + LHeC F2 HERA + LHeC F2, FL (Q2 = 2 GeV2) Including LHeC data in NNPDF DGLAP fit approach … … sizeable improvement in error on low x gluon when both LHeC F2 & FL data are included. … but would DGLAP fits fail if non-linear effects present? Can Parton Saturation be Established in ep @ LHeC? Simulated LHeC F2 and FL data based on a dipole model containing low x saturation (FS04-sat)… … NNPDF (also HERA framework) DGLAP QCD fits cannot accommodate saturation effects if F2 and FL both fitted [Rojo] Conclusion: clearly establishing non-linear effects needs a minimum of 2 observables … (F2c may work in place of FL)… What is Initial State of LHC AA Collisions? Gluons from saturated nuclei Glasma? • Very limited x, Q2 and A range for F2A so far (unknown for x <~ 10-2, gluon very poorly constrained) • LHeC extends kinematic range by 3-4 orders of magnitude with very large A QGP Reconfinement [d’Enterria] Current Knowledge: Nuclear Parton Densities Ri = Nuclear PDF i / (A * proton PDF i) First Study of Impact of e-Pb LHC data [Paukkunen, Armesto … in progress] • Striking effect on quark sea and gluons in particular • High x gluon uncertainty remains large • Now working on flavour decomposition 39 What about Diffraction? Additional variable t gives access to impact parameter (b) dependent amplitudes Large t (small b) probes densest packed part of proton? c.f. inclusive scattering probes median b~2-3 GeV-1 Dipole Model of J/y Photoproduction e.g. “b-Sat” Dipole model [Golec-Biernat, Wuesthoff, … “eikonalised”: with impact-parameter dependent saturation “1 Pomeron”: non-saturating Bartels, Teaney, Kowalski, Motyka, Watt] [Watt] [2 years in low x configuration] • Significant non-linear effects expected even for t-integrated cross section in LHeC kinematic range. • Data shown are extrapolations of HERA power law fit for Ee = 150 GeV… Satn smoking gun? Elastic J/y Production more Differentially J/y photoproduction double differentially in W and t … Cross sec probes to xg ~ 6.10-6 Q2 ~ 3 GeV2 ~ my2/4 Ee = 50 GeV, 1o acceptance, L=2 fb-1 Precise t dependence will help to reveal satn effects! Also possible in several Q2 bins and for Upsilon, DVCS … Inclusive Diffraction Additional variables … xIP = fractional momentum loss of proton (momentum fraction IP/p) b = x / xIP (momentum fraction q / IP) Further sensitivity to saturation phenomena Diffractive parton densities in much increased range Sensitivity to rapidity gap survival issues Can relate ep diffraction to eA shadowing … Control for interpretation of inclusive eA data Diffractive Kinematic Plane at LHeC • Higher Ee yields acceptance at higher Q2 (pQCD), lower xIP (clean diffraction) and b (low x effects) • Similar to inclusive case, 170o acceptance kills most of plane Simulated Diffractive DIS Data • 5-10% data, depending on detector • DPDFs / fac’n in much bigger range • Enhanced parton satn sensitivity? • Exclusive production of any 1– state with Mx up to ~ 250 GeV X including W, Z, b, exotics? [Forshaw, Marquet, PN] 1o acceptance, 2 fb-1 F2D and Nuclear Shadowing Nuclear shadowing can be described (Gribov-Glauber) as multiple interactions, starting from ep DPDFs [Capella, Kaidalov et al.] [Diff DIS] [eA shadowing] … starting point for extending precision LHeC studies into eA collisions First Detector Concepts – Low x Optimised 217 250 250 177 217 [cm] HaC-Barrel-bwd HaC-Barrel-fwd 40 250 EmC-Endcap-bwd Bwd Tracking Fwd Tracking EmC-fwd EmC-Barrel EmC-insert-½-bwd EmC-bwd 10⁰ and 170⁰ 177 5⁰ and 175⁰ 4⁰ and 176⁰ 3⁰ and 177⁰ 2⁰ and 178⁰ 1⁰ and 179⁰ Central Tracking HaC-insert-½-fwd HaC-insert-½-bwd 20 40 60 112 40 EmC-insert-½-fwd EmC-Endcap-fwd [17m x 10m (smaller than ATLAS / CMS)] 289 Solenoid+Dipole • Full angular coverage, long tracking region 1o • Dimensions determined by synchrotron radiation fan • Modular Low material budget High precision • Technologies under discussion (lots of ideas!) First Detector Concepts – High Q2 Optimised 217 250 250 250 [cm] HaC-Barrel-bwd HaC-Barrel-fwd EmC-Endcap-bwd 40 177 217 EmC-Barrel EmC-insert-½-bwd 177 10⁰ and 170⁰ 5⁰ and 175⁰ 4⁰ and 176⁰ 3⁰ and 177⁰ 2⁰ and 178⁰ 1⁰ and 179⁰ HaC-insert-½-fwd Central Tracking HaC-insert-½-bwd 20 40 60 112 EmC-insert-½-fwd EmC-Endcap-fwd Low Beta Magnet 40 Low Beta Magnet + MagCal + MagCal 289 Solenoid+Dipole • Sacrifice low angle acceptance to beam focusing magnets • Calorimeter inserts slide inwards • 2 phases of operation a la HERA? • Alternatively 2 interaction points (RR only)? Schedule and Remarks • Aim to start operation by 2020/22 [new phase of LHC] cf HERA: Proposal 1984 – Operation 1992. LEP: Proposal 1983 – Operation 1989 • The major accelerator and detector technologies exist • Cost is modest in major HEP project terms • Steps: Conceptual Design Report, early 2011 Evaluation within CERN / European PP/NP strategy If positive, more professional effort torward a Technical Design Report 2013/14 • In an optimistic long term perspective, a 140 GeV electron linac beam coupled with a 16 TeV Super-LHC’ beam would -7 Summary • LHC is a totally new world of •energy and luminosity! LHeC proposal aims to exploit it for TeV lepton-hadron scattering … ep complementing next generation pp, ee facilities • Ongoing ECFA/CERN/NuPECC workshop has gathered many accelerator, theory & experimental colleagues … still lots to do, even for CDR! • Next major workshop planned for October ’10 .All ideas and involvement welcome! [More at http://cern.ch/lhec] Back-Ups Follow The TeV Scale [2010-2035..] pp W,Z,top Higgs?? New Particles?? New Symmetries? LHC ep High Precision QCD High Density Matter Substructure?? eq-Spectroscopy?? LHeC New Physics e+ettbar Higgs?? Spectroscopy?? ILC/CLIC CKM - superB Working Group Convenors Scientific Advisory Committee Organisation for the CDR Guido Altarelli (Rome) Sergio Bertolucci (CERN) Stan Brodsky (SLAC) Allen Caldwell -chair (MPI Munich) Swapan Chattopadhyay (Cockcroft) John Dainton (Liverpool) John Ellis (CERN) Jos Engelen (CERN) Joel Feltesse (Saclay) Lev Lipatov (St.Petersburg) Roland Garoby (CERN) Roland Horisberger (PSI) Young-Kee Kim (Fermilab) Aharon Levy (Tel Aviv) Karlheinz Meier (Heidelberg) Richard Milner (Bates) Joachim Mnich (DESY) Steven Myers, (CERN) Tatsuya Nakada (Lausanne, ECFA) Guenther Rosner (Glasgow, NuPECC) Alexander Skrinsky (Novosibirsk) Anthony Thomas (Jlab) Steven Vigdor (BNL) Frank Wilczek (MIT) Ferdinand Willeke (BNL) Accelerator Design [RR and LR] Oliver Bruening (CERN), John Dainton (CI/Liverpool) Interaction Region and Fwd/Bwd Bernhard Holzer (DESY), Uwe Schneeekloth (DESY), Pierre van Mechelen (Antwerpen) Steering Committee Detector Design Peter Kostka (DESY), Rainer Wallny (UCLA), Oliver Bruening (CERN) John Dainton (Cockcroft) Albert DeRoeck (CERN) Stefano Forte (Milano) Max Klein - chair (Liverpool) Paul Laycock (secretary) (L’pool) Paul Newman (Birmingham) Emmanuelle Perez (CERN) Wesley Smith (Wisconsin) Bernd Surrow (MIT) Katsuo Tokushuku (KEK) Urs Wiedemann (CERN)) Frank Zimmermann (CERN) Alessandro Polini (Bologna) New Physics at Large Scales George Azuelos (Montreal) Emmanuelle Perez (CERN), Georg Weiglein (Durham) Precision QCD and Electroweak Olaf Behnke (DESY), Paolo Gambino (Torino), Thomas Gehrmann (Zuerich) Claire Gwenlan (Oxford) http://cern.ch/lhec Physics at High Parton Densities Nestor Armesto (Santiago), Brian Cole (Columbia), Heavy Quarks: HERA LHC • HERA HF information limited by kinematic range and lumi (reasonable charm, some beauty, almost no strange) • Crucial for understanding LHC initial state for new processes (e.g. bbbar->H) and backgrounds. Higgs <-SM MSSM-> • LHC predictions rely strongly on extrapolations and pQCD (e.g. CTEQ: 7% effect on W,Z rates varying HF treatment). pn 3.8m Luminosity: Ring-Ring N p 1.7 1011 N p Ie I m L 8.31032 e cm2s1 4e pn b px b py 50mA b px b pn p(x,y ) e(x,y ) b px 1.8m b py 0.5m 4 P 100GeV Ie 0.35m A MW E e Ie = 100 mA 1033 likely klystron installation limit Synchrotron rad! 1033 can be reached in RR Ee = 40-80 GeV & P = 5-60 MW. HERA was 1-4 1031 cm-2 s-1 huge gain with SLHC p beam F.Willeke in hep-ex/0603016: Design of interaction region for 1033 : 50 MW, 70 GeV May reach 1034 with ERL in bypasses, or/and reduce power. R&D performed at BNL/eRHIC cf also A.Verdier 1990, E.Keil 1986 Luminosity: Linac-Ring pn 3.8m P P / MW N p 32 2 1 L 110 cm s 4e pn b * E e E e /GeV N p 1.7 1011 b * 0.15m Ie 100m A Ie = 100 mA LHeC as Linac-Ring version can be as luminous as HERA II: High cryo load to CW cavities s 2TeV P GeV MW E e 4 1031 can be reached with LR: Ee = 40-140 GeV & P=20-60 MW LR: average lumi close to peak 140 GeV at 23 MV/m is 6km +gaps Luminosity horizon: high power: ERL (2 Linacs?) Geometric Scaling at the LHeC LHeC reaches t ~ 0.15 for Q2=1 GeV2 and t ~ 0.4 for Q2=2 GeV2 HERA Limit for Q2>2 GeV2 Some (though limited) acceptance for Q2 < Q2s with Q2 “perturbative’’ Could be enhanced with nuclei. (1 fb-1) Q2 < 1 GeV2 accessible in special runs? Azimuthal (de)correlations between Jets [Jung] Forward Instrumentation and Jets [Jung] x range (and sensitivity to novel QCD effects) strongly depend on q cut Similar conclusions for Df decorrelations between jets High x Partons Limiting LHC Searches Some BSM scenarios give deviations in high mass dijet spectra … e.g. a model with extra dimensions … S. Ferrag, hep-ph/0407303 … in this example, high x PDF uncertainties reduce sensitivity to compactification scales from 6 TeV to 2 TeV for 2XDs Structure with Leading Neutrons [Bunyatyan] (RAPGAP MC model, Ep=7TeV, Ee=70GeV) • With qn < 1 mrad, similar xL and pt ranges to HERA (a bit more pt lever-arm for flux). • Extentions to lower b and higher Q2 as in leading proton case. F2 At b<5.10-5 (cf HERA reaches b~10-3) (y=0.02) (qe=175o) (y=1) Also relevant to absorptive corrections, cosmic ray physics … Is HERA Finished? – H1 high pt Summary … perhaps yes for searches … • No significant BSM signals • Detectors and physics processes well understood! The Standard Model & HERA part as good friends! HERA Input to LHC • Unprecedented low x and high Q2 coverage in DIS • HERA + QCD factorisation parton densities in full x range of LHC rapidity plateau DGLAP • Well established `DGLAP’ evolution equations generalise to any scale (for not too small x) e.g. pp dijets at central rapidity: x1=x2=2pt / s LHeC Kinematics for Low x Investigations Access to Q2=1 GeV2 in ep mode for all x > 5 x 10-7 IF we have acceptance to 179o Without low b magnets ~ 1 fb-1 / yr ample for most low x studies … definitive low x facility! parton saturation novel QCD evolution Relations to confinement? … Strong Coupling Constant Simulation of as measurement at LHeC 1/a as least known of coupling constants Grand Unification predictions suffer from as fine structure DIS tends to be lower than world average weak LHeC: per mille accuracy indep. of BCDMS. Challenge to experiment and to h.o. QCD strong MSSM - B.Allnach et al, hep-ex/0403133 ? +pol J.Bluemlein and H. Boettcher, arXiv 1005.3013 (2010) Can DGLAP adjust to fit LHeC sat models? [Forshaw, Klein, PN, Perez] • Attempt to fit ZEUS and LHeC saturated pseudo-data in increasingly narrow (low) Q2 region until good fit obtained • Use dipole-like (GBW) gluon parameterisation at Q02 Q2 = 2 GeV2 Q2 = 10 GeV2 Q2 = 5 GeV2 l x C 2 2 xg (x, Q0 ) = Ag 1 exp Bg log (1 x) g x0 Q2 = 20 GeV2 • Fitting F2 only, a good fit cannot be obtained beyond the range 2 < Q2 < 20 GeV2 • This fit fails to describe FL Q2 = 2 GeV2 Q2 = 50 GeV2 (even faster failure with CGC LHeC pseudo-data) Q2 = 5 GeV2 A high x Detector Acceptance Consideration • Considerably more asymmetric beam energies than HERA! - Hadronic final state at newly accessed lowest x values goes central or backward in the detector - As x grows at fixed Q2, hadronic final state is boosted more and more in the forward direction … and hadrons are needed for good kinematic reconstruction as x gets large & electron method resolution deteriorates • Ideally need sensitivity to energy flow in outgoing proton direction for hadrons to ~1o 2.2 ctd) eA models compared with pseudodata [Armesto, Tywoniuk … in progress] EPS09 bands reasonable estimates, but no direct constraints LHeC pseudodata show F2 would give a first real and strong constraint on nuclear F2 ratio At low x FL data also studied 68 Developing a Combined Function “Magcal”? [Greenshaw] … also potentially interesting for medical physics and elsewhere? … could even think of doing the same with solenoids / toroids? Use scintilation of liquid He to get signal?… … Calo is all edges!… What sort of resolution is achievable? What is influence on final beam focus? …? LHeC J/y & U Photoproduction Simulation • Simulated data with heavy vector meson decays to . • Detector acceptance to within 1o of beampipe, • Lumi = 2 fb-1 (2 years) Ee = 50 GeV p J/y p pUp Precise measurements (even for U) well into sensitive region e.g. NNPDF study of low Q2 NLO DGLAP • Fit HERA data in limited regions above lines of Q2 > Ax-0.3 backwards evolve to lower scales and compare 2 • Signed pulls show backward evolution consistently above data … something happens, but not easily interpreted … 71 Parton Saturation after HERA? e.g. Forshaw, Sandapen, Shaw hep-ph/0411337,0608161 … used for illustrations here Fit inclusive HERA data using dipole models with and without parton saturation effects FS04 Regge (~FKS): 2 pomeron model, no saturation FS04 Satn: Simple implementation of saturation CGC: Colour Glass Condensate version of saturation • All three models can describe data with Q2 > 1GeV2, x < 0.01 • Only versions with saturation work for 0.045 < Q2 < 1 GeV2 … any saturation at HERA not easily interpreted partonically Reminder : Dipole models • Unified description of low x region, including region where Q2 small and partons not appropriate degrees of freedom … T ,L *p ( x, Q ) 2 dz d r 2 y T ,L * 2 ( z, r, Q ) dipole ( x, r, z) 2 • Simple unified picture of many inclusive and exclusive processes … strong interaction physics in (universal) dipole cross section dipole. Process dependence in wavefunction Factors • qqbar-g dipoles also needed to describe inclusive diffraction Forward and Diffractive Detectors • Very forward tracking / calorimetry with good resolution … • Proton and neutron spectrometers … • Reaching xIP = 1 - Ep’/Ep = 0.01 in diffraction with rapidity gap method requires hmax cut around 5 …forward instrumentation essential! • Roman pots, FNC should clearly be an integral part. - Also for t measurements - Not new at LHC - Being considered integrally with interaction region hmax from LRG selection … DVCS at LHeC [Favart, Forshaw, PN] (stat errors only) (1o acceptance) Statistical precision with 1fb-1 ~ 2-11% With F2, FL, DVCS could help establish saturation and distinguish between different models which contain it? HERA Cleaner interpretation in terms of GPDs at larger LHeC Q2 values